The present invention relates to a method and a device for feeding flat items to individualization, for example individualization for creating a regularly clocked stream of items, i.e. a stream in which single items are conveyed at regular distances or overlapping each other in a regular manner.
Flat items are individualized for processing, whereby single items are separated in succession from a group of items and are supplied to processing individually in a stream of items. In order to achieve continuous processing, the group of items serves normally as a buffer of items between the individualization and the supply of the items. This means that the group of items comprises a number of items varying within limits. The limits are such that there are sufficient items in the group to allow uninterrupted feeding to the individualizing process during expected supply gaps and to be able to absorb interruptions of the individualizing process without generating disturbances. The supply of items to the group of items may take place in batches or substantially continuously. The group of items from which the items are individualized is complemented regularly or, if required, with a plurality of items (batch) or items are continuously of, if required, added in form of a substantially continuous stream, for example a scaled stream.
For flat items it is obvious to use a stack of items as a group serving as buffer from which items are individualized, a stack being understood to be a formation in which the main surfaces of the flat items lie against each other. Items are removed individually (individualized) from the one face of the stack while items are added to the other face of the stack, either in stacked form (batch-wise feeding) or in a quasi-continuous stream (e.g. scaled stream).
In the further processing of printed products, many devices for individualizing printed products from stacks are known, to which devices the products are supplied in batches or continuously. The devices comprise guide means for guiding the buffer stack and conveying means for conveying the products in the buffer stack towards the individualization. The devices also include means for separating single printed products from the one end of the guide means and means for supplying printed products to the opposite end of the guide means. The separating means are usually arranged stationary and the supply means are at least partly movable in the direction of the stack axis (perpendicular to the flat extension of the products), and are adaptable to a varying number of items in the stack (varying stack height).
Depending on the application and according to the characteristics of the items to be individualized, the buffer stacks have rather a standing position (items lie on top of each other with substantially horizontal, flat extension, the stack axis is substantially vertical) or rather a lying position (items stand on one of their edges or narrow sides adjacent to each other with a substantially vertical, flat extension, stack axis horizontal or oblique). In many cases gravity is at least partly exploited for maintaining the stack order and/or for conveying the items toward individualization. In all cases, there are forces for guiding and/or conveying the items. These guiding and/or conveying forces are transmitted via the items in the buffer stack. For preventing such force transmission to have a negative effect on the order of the items in the stack, it is necessary to dimension the forces correspondingly, to adapt the guide means correspondingly, and/or to submit the items to corresponding conditions regarding their mechanical characteristics.
It shows that flat items which all have a substantially identical and well defined flat extension but have, within limits, an irregular and/or changing thickness, (i.e. flat items which can not be arranged in free stacks at all or only very restrictedly), can only be individualized from stacks at very restricted speeds when using known individualizing devices. This is, in particular, due to the fact that such items, especially in a guided stack, have more or less unstable positions and these positions become even more unstable with the transmission of forces via the items and thereby cause stack disturbances.
Items that are difficult to be stacked and thus difficult to be individualized from a stack are, for example, sample bags such as are often found glued into printed products for advertising purposes or added to printed products in other manners. For adding the sample bags to the printed products they need to be individualized from groups. Such sample bags typically consist of two blanks of paper or two blanks of plastic film, which two blanks are connected to each other around their edges forming a cushion shaped cavity between their center areas. The sample bags may carry samples of liquid, paste-like, powdery or granular products, or also soft items (e.g. moisture towels) or small items moving freely in the cavity of the sample bag. This kind of sample bag normally has a fairly well defined, hardly changing flat extension, i.e. it is e.g. square, rectangular or circular and it has sufficient stiffness to be able to stand on one edge when correspondingly supported. Perpendicular to its flat extension however, the sample bag comprises a thickness profile, which cannot only differ from item to item but which can also change depending on handling.
Free stacking of such sample bags is hardly possible or, if possible, only with very small stack height. In a guided stack (e.g. standing stack in a stack shaft or lying stack in a stack channel) it is hardly possible to transmit forces across a larger number of such bags. The positions of the individual bags in the stack are irregular and are not predictable.
In the publication EP-0739822 (or U.S. Pat. No. 5,735,107) it is suggested to stabilize the form of sample bags as described above in order to adapt them to easier stacking and thus easier individualization from a stack. Form stabilization is achieved by stiffening and thickening the bag edges such that they give the sample bag a stable frame by which the bags become easily and stably stackable. Sample bags stabilized in this manner can be individualized with similar methods and similar devices, and at similar high individualizing speeds, as is the case for other simple and stable items such as, for example, postcards.
The above described characteristics regarding stacking are not only a feature of the described sample bags but also of differently shaped bags, which are actually flat but have an easily deformable and/or movable content as well as of at least partly flat items with an actually unchangeable but irregular thickness profile.
It is the object of the invention to create a method and a device for feeding to individualization flat items with the above mentioned characteristics rendering them difficult to be stacked, such that high individualizing speeds in the range of several ten thousand items per hour becomes possible. Furthermore, method and device are to be easily adaptable to different formats of item.
According to the inventive method the flat items are fed to individualization being arranged in a stack which is substantially lying (stack axis horizontal or oblique) and in which the items are arranged standing on one of their edges. This stack comprises, on its individualization-side, an individualizing stack and, on its supply-side, a pre-stack, whereby the items are individually removed (individualized) from the individualizing stack and are supplied in batches or substantially continuously to the pre-stack and whereby it is the pre-stack that mainly takes over the buffer function.
The individualizing stack is guided by stack guiding means and comprises a considerably smaller number of items than the pre-stack, whereby the number of items in the individualizing stack only varies within very tight limits, i.e. is kept as constant as possible. The pre-stack is also guided by stack guiding means, whereby also each individual item in the pre-stack is guided at least to a restricted degree. The number of items in the pre-stack is considerably larger than in the individualizing stack and due to the buffering function varies considerably more during operation than the number of items in the individualizing stack. The individualizing stack and the pre-stack further differ regarding order conditions, i.e. conditions imposed on the regularity of the item positions, which in the individualizing stack are considerably more important than in the pre-stack.
A device for carrying out the inventive method substantially comprises four regions: a supply region, a pre-stack region, an individualizing-stack region and an individualizing region, which regions follow each other as listed in conveying direction of the items.